THERMODYNAMIC PROPERTIES OF PROTACTINIUM HYDRIDES
Pressure - composition isotherms of the protactinium - hydrogen system were measured in the range of 10**-5 <= p <= 100 bar, 0 <= H/Pa < 3, 373 <= K <= 795 for increasing and decreasing H/Pa ratios. Large hysteresis was observed on hydriding and dehydriding. The shape of the isotherms and X-ray structure analysis indicate the existence of different phases. At H/Pa < 0.1 the metal is saturated with hydrogen (phase I). At 1.3 < H/Pa < 1.7 and temperatures above 550 K a second phase (phase II) with an unique fcc structure is observed. Another high temperature phase with beta-UH-3 related structure exists in the range 2.0 <= H/Pa <= 3.0. At temperatures below 500 K and 1.3 < H/Pa <= P 3.0 an alpha- UH-3 related solid solution (phase IV) is identified. In the regions 0.1 < H/Pa < 1.3 and 1.7 < H/Pa < 2.0 two phases coexist (2). For all compositions 1np-1/T-relationships are linear with a significant change in slope at about 550 K on hydriding. There are not enough data to confirm this difference in slope on dehydriding. Partial molar free enthalpies and entropies for selected compositions were calculated from the 1np-1/T functions and are reported.
Bibliographic Reference: 1ST INTERNATIONAL CONFERENCE ON THE CHEMISTRY AND TECHNOLOGY OF THE LANTHANIDES AND ACTINIDES, VENEZIA (ITALY) SEPT. 5-10, 1983 - WRITE TO CEC LUXEMBOURG, DG XIII/A2, POB 1907 MENTIONING PAPER E 31201 ORA
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Record Number: 1989122031500 / Last updated on: 1987-01-01
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